Degumming of silk



Patented May 19, 1936 UNITED STATES DEGUMMZINQ or SILK Henry Charles Olpin and George Holland Spondon, near Derby, England, assignors to 'Celanese Corporation of America, a corporation of Delaware No Drawing. Application December 16, 1933, Serial No. 702,792. In Great Britain January 4 Claims.

This invention relates to the degumming of silk and especially to the degumming of silk in association with other fibres liable to be adversely afiected by the treatments utilized in the degumming of silk materials.

The degumming of silk is of course an essential step in the manufacture of silk materials and is generally conducted after the silk has been incorporated into fabrics. If therefore the fabrics contain other materials, for, example artiflcial silk such as that made from cellulose acetate, it is essential that the degumming treatment should not be such as will adversely affeet the second-mentioned material. In the case of a fabric comprising both natural silk and cellulose acetate artificial silk the degumming of the natural silk presents a rather difllcult-prob-- lem, in that the conditions under which the natto operate at temperatures much over 80 -C. if

ural silk is most readily degummed; namely relatively high temperature and a fair degree of alkalinity, are decidedly prejudicial to cellulose acetate. High temperature of the degumming bath leads very easily to delustring of the cellulose acetate and it is therefore not practicable be effected in a reasonable time while avoiding saponification and/or delustration of the' cellulose acetate.

We have discovered that it is possible by pretreatment to render the gum of natural silk much more readily removable, particularly by aqueous liquids, and hence to render it possible to effect degumming by a treatment of moderate duration under conditions of alkalinity and tem-- perature which do not eifect any appreciable saponiflcation or delustration of cellulose acetate.

At the same time we have found that the rendering of the gum more readily removable may be eflected by the pretreatments without materially affecting either the silk itself or other materials, for example cellulose acetate, which may be in association therewith.

The pretreatment for rendering the gum more ,readily' removable very advantageously. consists of an alkaline treatment, preferably aqueous, at

ordinary temperature. The degree of alkalinity may be substantially greater than that which can be tolerated by the silk and/or any materials in association with the silk under the conditions of degumming. Materials so treated may then readily be degummed under much less vigorous conditions, for example of temperature and alkalinity, than are normally necessary to effect the degumming of silk within a reasonable duration. It is surprising that such a comparatively strong alkaline pretreatment has a marked effect on the ease with which degumming maysubsequently be efiected and yet may be so conducted as to avoid any material saponification of cellulose acetate.

Various alkalies may be employed as the alkaline ingredient of the pretreatment bath, for example sodium carbonate or trisodium phosphate. Particularly good results have been obtained, however, with caustic soda or other caustic alkali. The alkalinity of the pretreatment bath may vary within comparatively wide limits and very good results have been obtained by employing aqueous solutions containing from about 2-12 grams per litre and especially with solutions containing in the neighbourhood of 5 grams per litre of caustic soda. In the case of other alkalies, solutions of equivalent alkalinity may be employed. The duration of the pretreatment may likewise vary within comparatively wide limits. Thus, the pretreatment may be effected for about ten minutes when working on a small scale, or with advantage for a somewhat longer time when operating on a large scale. 7

.The subsequent degumming operation proper may thereafter be eifected in any desired manner, for example with soap solutions with or effected at temperatures not exceeding 80 C: and In.

under relatively weakly alkaline conditions. the case of materials containing cellulose acetate, the degumming operation may therefore be effected in a reasonable time without material a comparatively low temperature, for example delustring or saponifying of the cellulose acetate pretreatment baths in order to facflitate the softening action of the alkali and so render the treatment more effective and/or reduce its duration. The duration of the degumming treatment -will usually vary considerably according to the nature of the materials undergoing treatment,

and of course according to the temperature employed. In general a treatment of 1-2 hours is sufllcient to eifect. the requisite degree of degumming, though longer time may be required in the case, for example, of closely knitted or woven materials or materials containing highly twisted natural silk yarns. v

It is not essential to employ. entirely separate treatments for the alkaline prettehtment and for the degumming operation proper. If desired the materials may be entered into the cold alkaline pretreatment bath for the requisite period and the bath thereafter adjusted, as regards composition, concentration and temperature, in order to yield a degumming bath of the required characteristics. Thus, for example, the material may be entered into a 10:1 bath containing 5-10 grams per litre of caustic soda or an equivalent amount of other alkali, and the bath thereafter increased to 100:1' ratio by addition of water and the requisite soap or other agents required to complete the degumming bath, the temperature being then raised to that required to effect degumming. The materials are thus subjected 'to ture. If desired. the whole of the constituents 1 a relatively strongly alkaline treatment in the cold and thereafter to a degumming treatment of relatively low alkalinity at a higher temperarequired in the degumming bath may be contained in the pretreatment bath, though whe're the-degumming bath is to contain much soap, for example soap in the proportions indicated, the soap is preferably added after the pretreatment in view of the difliculty of dissolving the necessary quantity in the short pretreatment bath.

Though an alkaline pretreatment has been found particularly advantageous, other pretreatments adapted tosoften the gum on the silk and thereby render itreadily removable may be employed in place of or inaddition to the said alkaline treatment. Thus, if desired, the materials may be subjected'to a'short treatment with suitable enzymes capable of effecting a softeninl of the gum. I

As will be appreciated, the invention is of particular importance in connection with the degumming of silk in materials containing. both silk and cellulose acetate. Theutility of the invention is not however restricted to the treatment of such materials, thus for instance materials containing other esters of cellulose, for

example cellulose formats, propionate or butyrate, may similarly be treated or materials consisting solely of natural silk or 6115mm silk in association with other natural or artificial fibres;

The following examples illustrate the invention which is in no way limited thereby:-

Emmple 1 Hanks of a mixed yarn containing both natural silk and cellulose acetate filaments are treated in the cold for 10 minutes in a 10:1 weight/volume bath comprising grams sodium carbonate and 20 grams isopropyl naphthalene sodium sulphonate per litre. The bath is then diluted to 100:1 ratio and 5 grams of soap per litre of the dilute bath is added: the yarn is treated in the degumming bath so obtained for 1 hour 'at a temperature of 80 C. A complete degumming is attained with little-or no alteration to the cellulose acetate constituent of the yarn.

Example 2 /-Real silk hosiery containing cellulose acetate yarns as effect threads to the extent of 10% of the total weight is steeped for 10 minutes in the cold in a 10:1 weight/volume solution of 10 grams soda ash and 10 grams isopropyl naphthalene sodium sulphonate per litre. The bath is thereupon diluted to 100:1 weight/volume, 5 grams per litre of textile soap flakes is added, and the bath is raised to a temperature of 80 C. and maintained thereat till degumming is complete (1. e.

for about 1 hour). The goods are then washed ,out thoroughly and dried or otherwis treated as requisite.

- Example 3 A crepe fabric consisting of approximately equal parts of a cellulose acetate warp and a highly twisted natural silk weft, is suitably suspended from supporting sticks, and immersed for 10 minutes in a cold 10 gramsper litre caustic soda solution. The fabric is then rinsed thoroughly and immersed in a bath containing:

per litre Textilesoap I t 5 Soda ash e 1 Isopropylnaphthalene sodium sulphonate"-.. 1

The temperature is then raised slowly to 80 C. and-maintained thereat for 2 hours or till degumming is complete. After washing oil thoroughly the goods are ready for dyeing or other desired treatments.

- What we claim and desire to Patent is:-

1. Process for the degumming of natural silk in. materials comprising both natural silk and secure by Letters a cellulose ester, which comprises subjecting the materials to a pretreatment at approximately [atmospheric temperature with a solution of alkalinity equivalent to that of a sodium hydroxide'solution of concentration between 2 and 12 grams per litre, and thereafter subjecting them to a degumming operation.

2. Process for the. degumming of natural silk in materials comprising both natural. silk and cellulose acetate, which comprises subjecting the materials to a pretreatment at approximately atmospheric temperature with a solution. of

alkalinity equivalent to that of a sodium hydroxide solution of concentration between 2 and 12 grams per litre, and thereafter shbjecting them to a degumming operation.

3. Process for thefdegummins of natural silk in materials comprising both natural sflk and a cellulose ester, which comprises subjecting the materials to a pretreatment at approximately atmospheric temperature-with an aqueous solution of a substance selected fromthe group consisting of caustic alkalies and alkali metal carbonates, said solution having an alkalinity equivalent to that of a sodium hydroxide solution of concentration between 2 and 12 grams per litre. and thereafter subjecting them to a degumming operation.

4. Process for the degumming of natural silk in materials comprising both natural silk and cellulose acetate, which comprises subjecting the materials to a pretreatment at approximately atmospheric temperature with a solution of alkalinity equivalent to that oi! a sodium hydroxide solution of concentration of the order of 5 grams per litre, and thereafter subjecting them 5 to a degumming operation.

HENRY CHARLES OLPIN. GEORGE HOLLAND mus. 

